Spray a half-sheet baking pan with non-stick spray or line with parchment.
Preheat oven to 150˚ for about 5 minutes then turn off.
Combine water, sugar and yeast. Stir well. Allow to proof while you measure out the rest of the ingredients.
Place the egg whites in stand mixer and whip to soft peaks with the whisk beater.
Measure out the dry ingredients and mix together.
Measure out the vinegar and oil and set aside.
When the egg whites are whipped, change whisk beater to the paddle beater and add all the wet ingredients to the eggs. Mix slowly.
While mixer is running slowly, add dry ingredients to the mixer and blend on medium speed for 3 minutes. Mixture will be a thick batter.
Spread batter into prepared pan and spread the top smooth.
Use a pastry brush to spread olive oil, sprinkle with rosemary and course salt.
Place in oven and allow to rise for 30 minutes.
When the proofing is finished, set the temperature to 350˚ and bake for 45 minutes.
Bake focaccia until top is golden browned and bread is firm. Remove from oven and cool. Tear or cut apart to serve.